Not Applicable
Not Applicable
Not Applicable
The present invention relates to solenoid operated valves employed for controlling flow of pressurized hydraulic fluid to actuators in an hydraulic system in response to an electrical control signal, such as provided by a microcomputer. Solenoid operated pressure control valves are employed in a variety of applications; one such application being for the control of shifting clutch actuators in an automatic transmissions for motor vehicles.
Heretofore, electrically operated pressure control valves for controlling the shifting in an automatic transmission for a motor vehicle have employed a valving member configured as a spool with cylindrical valving lands provided thereon for controlling flow of hydraulic fluid between an inlet and a control or signal outlet port with pressure control provided by bleeding fluid through an exhaust outlet port which returns the flow to the source or sump.
In providing such an electrically operated pressure control valve for motor vehicle automatic transmission shift control, problems have been encountered in obtaining adequate pressure control over a wide range of flow required to provide the necessary shift actuator movement because of the magnetic characteristics of the actuating solenoid.
For a given level of solenoid electrical energization, the magnetic force on a typical solenoid armature varies non-linearly with respect to armature movement. As the armature reduces the working air gap with the stationary pole piece or flux collector, the magnetic force tends to increase exponentially thereby giving the resultant response of the valve spool connected to the armature undesirable valving characteristics. The exponential increase in the magnetic force causes prohibitively rapid opening and closing of the respective ports for given port and spool land configurations and thus renders proper control of the hydraulic pressure in the actuating circuit extremely difficult.
Accordingly, it has long been desired to provide a solenoid operated pressure control valve for controlling the flow of hydraulic fluid in an actuating circuit which provides a relatively long armature stroke with substantially linear response for a given level of solenoid energization and provides generally linear or proportional pressure control over the operating range of coil energization.
The present invention addresses the above described problem and provides a solenoid operated pressure control valve of the type having a spool moveable in a valve body for controlling flow from an inlet to an control or signal outlet port and to a bleed port for maintaining pressure control. The spool of the valving member in the present invention has a pair of spaced lands for controlling flow respectively to the control and exhaust port in response to spool movement by the solenoid armature. The solenoid is constructed to provide reduced magnetic flux at one end of the armature as the working air gap on a remote end of the armature is closed by a given level at coil energization. The flux is decreased at the one end of the armature by a reduced area portion of the flux collector which surrounds the distal end of the armature forming an annular air gap therebetween. The decrease in flux at the remote end of the armature results in a substantially linear force versus stroke characteristics for the solenoid upon coil energization at a given level. The resultant pressure at the control pressure outlet is thus generally proportionally changed with respect to changing coil energization.